Arrays

I'm learning how to use arrays in c++ with the Practical C++ Programming book from O'Reilly but now I have run into a problem.

Im working with Multidimensional arrays ie, n[3][3]. Im trying to make a 3*3 grid that displays any number from 0 - 9 but it's not allowed to have any of the same number. I have managed to get it to check each number in the different rows and columns. So if I have 3 in n[0][0] then the other numbers in row n[0][...] can't be a 3 and the other numbers in column n[...][0] can't be a 3. This part works fine but how can I get it to check that the number in n[0][0] is not the same as the number in n[1][1] or n[2][2] for example.